If anyone is still interested in this topic, I've created a wiki page on how to change the eMMC its filesystem:

http://wiki.maemo.org/Changing_the_eMMC_filesystem

I reformatted my /home as Reiser4 because of its transparent LZO compression support and the existence of a native kernel 2.6.28 patch. However, as it is not included in kernel-power I've oriented the wiki page as if you want to format the partition as ext4.

Additions to the wiki page are welcome of course